NASA Marshall’s Skylab Reuse Study (1977)

Image: NASA

On 14 May 1973, the last Saturn V to fly, designated SA-513, launched the Skylab Orbital Workshop (OWS) into a 435-kilometer-high orbit about the Earth. Flight controllers soon realized that the 100-ton space laboratory was in trouble. Although they did not know it at the time – Skylab had launched into dense clouds, so could not be imaged during most of its ascent – 63 seconds after liftoff a design flaw had caused Skylab’s meteoroid shield to rip away. Shield debris had jammed one of the workshop’s two main electricity-producing solar arrays. The other array remained attached to Skylab’s side only at its hinge (forward) end.

Skylab launch. Image: NASA

Shield debris had pummeled SA-513, tearing at least one hole in the tapered interstage adapter that linked its S-II second stage with the OWS. It also apparently damaged the system for separating the cylindrical adapter that linked the S-II to the S-IC first stage. The adapter, meant to separate shortly after the spent S-IC, remained stubbornly attached to the S-II all the way to orbit.

After the S-II’s five J-2 engines shut down, forward-facing solid-propellant rockets ignited to push the spent stage away from Skylab. Their plumes blasted open and tore away the loose solar array. Ironically, the jammed array probably survived because it was tied down by meteoroid shield debris.

Without the protection of the reflective meteoroid shield, temperatures within Skylab’s 11,303-cubic-foot pressurized volume soon soared, raising fears that its air would become tainted by outgassing from materials on board, film would be ruined, and food spoiled. Meanwhile, maneuvers designed to cool Skylab’s interior tended to starve it of electricity, for they turned away from the Sun the four “windmill” solar arrays on the Apollo Telescope Mount (ATM), the beleaguered space laboratory’s only functioning electricity source.

NASA immediately began a Skylab rescue effort. Engineers developed deployable sunshields and tools for freeing the stuck main array, flight controllers carefully maneuvered Skylab to maximize the amount of electricity the ATM arrays could produce while reducing temperatures on board as much as possible, and the first crew meant to board Skylab (designated Skylab 2 by NASA) hurriedly trained to become orbital repairmen.

Skylab 2 astronauts Joe Kerwin (left), Charles “Pete” Conrad, and Paul Weitz became the first crew to refurbish Skylab after it was damaged during launch. Image: NASA

On 25 May, the Skylab 2 crew of Pete Conrad, Paul Weitz, and Joe Kerwin lifted off in an Apollo Command and Service Module (CSM) atop a Saturn IB rocket. After a failed attempt to pull open the one remaining main solar array with a hook extended from the open CSM hatch, they docked with and entered Skylab, then deployed a sunshield through an experiment airlock. Temperatures began to fall, but the Orbital Workshop remained starved for electricity. On 7 June, Conrad and Kerwin succeeded in forcing open the surviving main solar array, saving not only their own 28-day mission, but also the 59-day Skylab 3 and 84-day Skylab 4 missions.

The Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off 28 July. During their 6 August spacewalk, Lousma and Garriott deployed an improved sunshield. The Skylab 4 crew of Jerry Carr, William Pogue, and Ed Gibson boarded the laboratory on 16 November. Carr and Gibson mounted a meteoroid collector on an ATM strut during their spacewalk on 3 February 1974, in the hope that a Space Shuttle crew might retrieve it as early as 1979. When the Skylab 4 crew undocked on 8 February 1974, Skylab was expected to remain aloft until 1983, when atmospheric drag would cause it to fall back to Earth. They left Skylab’s airlock hatch closed but not latched so that it could provide entry for future visitors.

On 10 June 1977, former Skylab Deputy Director John Disher, NASA’s Director of Advanced Programs, directed NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, to conduct an in-house study of the feasibility of reusing Skylab in the Space Shuttle program. On 16 November 1977, MSFC engineers J. Murphy, B. Chubb, and H. Gierow presented results of the study to NASA Associate Administrator for Space Flight John Yardley. Before coming to NASA in 1974, Yardley had managed Skylab assembly at McDonnell Douglas, the Orbital Workshop’s prime contractor.

The MSFC engineers first assessed Skylab’s condition. They reported that when the Skylab 4 crew returned to Earth, the Orbital Workshop’s water system contained 1930 pounds of water (enough to supply three men for 60 days). The water, they said, probably remained potable, but could have developed a bad taste. If not still potable, it could be used for bathing. In any case, the Skylab water system included resupply points, so a Space Shuttle crew could replenish it if water transfer equipment were developed.

The oxygen/nitrogen supply remaining on Skylab was probably sufficient to supply three men for 140 days at Skylab’s operating pressure of five pounds per square inch, the MSFC engineers estimated. The ventilation and carbon dioxide removal systems were almost certainly functional. Even if they were not, their most important components were designed to be replaceable in space.

The MSFC engineers also assessed Skylab’s electrical power system. They estimated that the main solar array Conrad and Kerwin had freed could still generate between 1.5 and 2.5 kilowatts (KW) of electricity, and that the batteries it had charged, located in Skylab’s Airlock Module, were probably still usable. The batteries for the ATM arrays, on the other hand, were almost certainly frozen. They recommended that controllers reactivate the main array electrical system from the ground before the first Shuttle visit, and that any effort to revive the ATM electrical system be left until a later time.

More problematic than the electrical system was the attitude control system, which relied on a trio of Control Moment Gyros (CMGs) to turn Skylab so that, among other things, it could point its solar arrays at the Sun. One CMG had failed and another showed signs of impending failure. In addition, Skylab’s guidance computer was probably dead after being subjected to “extreme thermal cycling.” The Orbital Workshop’s thruster system, on the other hand, was probably operational with about 30 days of propellant remaining.

Finally, the MSFC team looked at Skylab’s cooling system, which had leaked while the astronauts were on board and had probably frozen and ruptured since the last crew returned to Earth. They called “serviceability of [the] cooling system. . .the most questionable area” as far as Skylab’s reusability was concerned, but added that “any inflight ‘fixes’ should be well within the scope of crew capability.”

The MSFC engineers then proposed a four-phase plan for reactivating and reusing Skylab. The target date for the first Phase I milestone had already passed by the time they briefed Yardley: they called for an October 1977 decision on whether Skylab should be reboosted to a higher orbit, extending its orbital lifetime until about 1990, or deboosted so that it would reenter over an unpopulated area.

Assuming that NASA decided to reboost Skylab, then a ground reactivation test would occur between June 1978 and March 1979. If the reactivation test was successful, then a Space Shuttle Orbiter would rendezvous with Skylab during the Shuttle Program’s fifth Orbital Flight Test mission in February 1980. The Orbiter would conduct an inspection fly-around, then deploy an unmanned Teleoperator spacecraft from its payload bay. Using a control panel on the Shuttle, the astronauts would guide the Teleoperator, which would carry an Apollo-type probe docking unit, to a docking with the front docking port on Skylab’s Multiple Docking Adapter. The Teleoperator would then fire its thrusters to raise Skylab’s orbit. Its work done, it would then detach, freeing up the front port for Phase II of MSFC’s plan.

Image: NASAPhase II would begin in March 1980, when NASA would initiate development of Skylab refurbishment kits, a 10-foot-long Docking Adapter (DA), and a 25-KW Power Module (PM). The DA would include at one end an Apollo-type probe docking unit for attaching it to Skylab’s front port and at the other end an Apollo-Soyuz-type androgynous unit to which Shuttle Orbiters and the PM could dock.

The first refurbishment kit and the DA would reach Skylab on board a Shuttle Orbiter in January 1982. During the same mission, spacewalking Shuttle astronauts would fold two of the four ATM solar arrays to improve clearance for visiting Orbiters and would retrieve the meteoroid experiment the Skylab 4 astronauts had left on the ATM.

A second Shuttle visit in August 1983 would bring additional refurbishment kits and would repair Skylab’s damaged cooling system plumbing. As time allowed, the Phase II crews would perform undefined “simple passive experiments” on board Skylab and would collect samples of its structure for analysis on Earth.

Phase III would begin in March 1984 with delivery of the PM and any remaining refurbishment kits, the MSFC engineers told Yardley. Using the Shuttle’s Remote Manipulator System robot arm, astronauts would lift the PM from the Orbiter’s payload bay and turn it 180° so that it protruded forward well beyond the Orbiter’s nose. They would then dock one of the PM’s three androgynous docking units to an identical unit at the front of the Orbiter’s payload bay. The Shuttle would use another of the PM’s docking units to dock with the DA on Skylab.

Following docking with Skylab, the astronauts would deploy the PM’s twin solar arrays and thermal radiators, link it to Skylab’s systems by cables extended through open hatchways or installed on the hull during spacewalks, and power up the PM’s three CMGs to replace Skylab’s crippled attitude control system. The Orbiter would then undock from the PM, leaving it attached permanently to Skylab, and NASA would declare the revived and expanded Orbital Workshop to be fully habitable.

Skylab in Phase III configuration, c. 1984. Image: Junior Miranda

Phase III would continue with the first in a series of 30-to-90-day missions aboard Skylab. During these, a Shuttle Orbiter carrying a Spacelab module in its cargo bay would remain docked with the Orbital Workshop. The astronauts would work in the Spacelab module, take advantage of Skylab’s large pressurized volume to perform “simple experiments” requiring more room than Shuttle and Spacelab could provide (for example, preliminary space construction experiments), and begin building up stockpiles of food, film, clothing, and other supplies on board. Another 30-to-90-day mission would see the astronauts refurbish and use selected Skylab science experiments, install new experiments based on Spacelab experiment designs, and stockpile more supplies. Between these missions, the new and improved Skylab would fly unmanned.

The MSFC engineers told Yardley that the volume available to a crew on board a Shuttle Orbiter without a Spacelab module in its payload bay would total only 1110 cubic feet. Adding a Spacelab would increase that to about 5100 cubic feet. This was, however, less than half the pressurized volume of Skylab. For a mission including a Shuttle Orbiter, Spacelab module, and Skylab, the total volume available to the crew would exceed 16,400 cubic feet.

Image: Junior Miranda

They were not specific about what Skylab would be used for when Phase IV began in mid-1986, though they did offer several intriguing possibilities. Shuttle Orbiters might, for example, attach Spacelab modules and experiment pallets to the third docking port on the PM. A Shuttle External Tank might be joined to Skylab to serve as a strongback for large-scale space construction experiments using a mobile “space crane.” The experiments might include construction of a large space power module or a multiple beam antenna. A new “floor” might be assembled within Skylab, enabling it to house up to nine astronauts. As NASA developed confidence in the revived space laboratory’s health, manned missions on board Skylab without a Shuttle Orbiter present might commence, leading to permanent manning and “support [of] major space operations.”

The MSFC engineers did not estimate the cost of Phases I and IV of their plan, though they did provide a (perhaps optimistic) pricetag for Phases II and III. Their estimate did not include Space Shuttle transportation and contractor study costs. In Fiscal Year (FY) 1980, NASA would spend $2 million each on Phases II and III. This would climb to $5 million for Phase II and $3.4 million for Phase III in FY 1981. FY 1982, the plan’s peak funding year, would see $4.5 million spent on Phase II and $10.2 million spent on Phase III. In FY 1983, NASA would spend $2.5 million to close out Phase II and $12 million to continue Phase III. The following year it would spend $9.1 million on Phase III. Phase III closeout in FY 1985 would cost $4.5 million. Phase II would cost a total of $14 million, while the more ambitious Phase III would total $41.2 million. Phases II and III together would cost $55.2 million.

MSFC’s presentation to Yardley concluded with a call for more in-house and contractor studies in FY 1978. McDonnell Douglas and Martin Marietta subsequently began more detailed Skylab reuse studies, the former under supervision of NASA Johnson Space Center in Houston, Texas, and the latter under MSFC supervision. The Martin Marietta and McDonnell Douglas studies will be discussed in forthcoming posts.